The present invention relates to a structure for supporting a roof made of French type tiles or the like, such as Marseille type tiles, Holland type tiles, etc. normally made of ceramics or of any other suitable material These tiles are low porosity, rectangular rigid pieces, shaped with outstanding ribs, longitudinal or parallel to the larger sides. These ribs mate with the two traverse smaller sides or edges which have grooves or engagement portions and emerging teeth varying in accordance with the tile type, but always for engaging each tile with adjacent ones. The tiles of each row are placed with their lower smaller edges on the upper edges of the next lower tile row.
In practice, these tiles may have at least a through hole close to their upper edge for connecting these tiles on a wooden purlin forming part of the structure supporting the tiles, by means of nails or wire fasteners. Emerging from the bottom of the same upper smaller edge there exist normally two teeth or a rib which rest laterally on the purlins to avoid the downward slip of the tiles.
This structure is conventionally comprised by two main portions: the supporting structure per se, comprising trusses, rafters, beams, etc. and, secondly, by a direct supporting and fastening device, commonly comprised of horizontal purlins or strips, placed as per parallel lines, supported by the above mentioned rafters or the like, and having a traverse slope resulting from the slope of the rafters.
The above mentioned parallel purlins or strips are engaged to rafters through nails or screws, and the space therebetween is somewhat smaller than the length of the tile, so as to allow each tile to be supported by mating simultaneously with each traverse smaller edge, on corresponding purlins. Therefore, the upper edge of the next lower row of tiles rests on each purlin, and the lower edge of the next upper row rests on the same edge.
Consequently, as is conventional, margin portions of the upper traverse edges of the tiles in each row are engaged by nails or wire laces; and supported laterally by the teeth or a rib on the bottom of the tile in turn, the margin portions of the lower edges of the tiles on the next upper row rest and fit, due to their weight, on these portions. Nevertheless, there are some cases in which fastening means are not used and tiles are simply superimposed and only held in place by the teeth, thus resulting in several disadvantages.
Generally, the above mentioned structures, such as trusses, rafters, purlins, etc. are made of wood. Such wood may slip or move due to load action or due to the fact that it is green, which causes scratches and/or breakage of the tiles, or any other undesired abnormality.
Among the mentioned engaging and supporting resources, the following are the two preferred alternatives, namely: (a) sizing the purlins supported by rafters, and separating the rafters so as to assure sufficient supporting strength against torsion and bending in order to avoid tile displacement or, at least, to assure that tile displacement does not affect the stability thereof. This stands for an oversizing of values resulting from the use of conventional calculated strains according to different types of wood; and (b) placing a continuous planking, preferably a tongue and groove planking, between the rafters or the like, under the above mentioned purlins, thus strengthening the structure against movement of the purlins.
When employing alternative (b), often a layer of waterproof material is added, preferably an asphalt impregnated felt, which is applied perfectly flat on the planking, in order to form a barrier against water which may have passed through tiles or cracks thereof.
This waterproof coating is less suitable when tiles are directly engaged on the supporting and engaging purlins, transversely to rafters, such as in alternative (a); but in such cases aesthetics of the roof are affected, unless it is covered by some means such as paint, etc.
In order to avoid tile displacement, it is known in the art to use structural members, including supporting purlins, made of metal, on which tiles rest. In such a case, wire fastening or nailing to prevent relative displacement between tiles and purlins is unavoidable. Due to the fact that all tiles should be wire fastened or nailed, operators' movements may result in further cracks or breakage. Besides, this operation involves delays and increases in man hours, and therefore the cost is notably increased.